実際にやってみないとわからない。
You won't know unless you actually try it.
His story really happened.
in practice; practically
Focuses on the practical, real-world situation as opposed to theory or ideals. Often used when contrasting with what is supposed to happen.
See also: 実際
It's possible in theory, but in practice it's difficult.
When I actually tried it, it turned out to be surprisingly easy.
It's better to see the painting in person rather than in a photo.
I actually went to the site to investigate.